PCA9614 SCL and SDA hang at 0 when bus is in idle

i'm using the PCA9614 in the configuration of fig.6 of the datasheet (at page 10) with R1 = 604 Ohm and R2 = 121 Ohm with Vss1 not conneted to Vss2 and Vddb1 not connected to Vddb2.

The device is communicating correctly with the devices on the bus but after a while the communication stop, after that is impossible to recover the device, seems broken; i made more investigation and seems that the idle condition (D+ > D-) on the bus is not seen and the SCL line and SDA line hang at 0, like if the bidirectional function of the device is broken.

I can't understand where is the problem, how the device can break in this way we are missing something in the hardware?